The field of the invention relates to medical instruments and more specifically to a cannula for use with laparoscopic instruments to permit the passage of laparoscopic instruments through the cannula while maintaining a seal around the instruments.
The use of cannulas in laparoscopic surgery is well known. In laparoscopic surgery an incision is made by means of a trocar and the abdomen is filled with carbon dioxide gas. The cannula which maintains the incision open to receive surgical instruments must be kept closed to prevent the escape of the gas. Many prior art cannulas utilize a trapdoor within the housing of the cannula with the trapdoor being spring pressed to a closed position The trapdoor opens when an instrument is passed through the cannula. However, quite frequently the laparoscopic instrument has a curved tip or other structure which will catch on the trapdoor and thus prevents the removal of the instrument from the cannula. Cannulas of this type are shown in the Moll et al U.S. Pat. No. 4,654,030 and the Deniega et al U.S. Pat. No. 5,066,288.
Prior art cannulas are designed with flexible seals to permit passage of instruments through the cannula without permitting gas within the abdominal cavity from leaking through the cannula. However, such seals are generally designed for a single size of instrument and when instruments of varying diameters are used, the seals are ineffective and permit the escape of gas from the abdominal cavity. The present invention overcomes the above-noted disadvantages of prior art cannulas.